For the ice cubes:
For the lemonade:
Add a few fresh berries to each well of an ice cube tray. Fill the wells with water and freeze until solid.
In a small saucepan, combine the lemon juice and sugar over medium heat. Let cook, stirring occasionally, until the sugar has dissolved completely. Transfer to a large liquid measuring cup, cover and chill until ready to serve.
To serve, place a few of the berry ice cubes in each serving glass. Add 2 cups of the sparkling water to the chilled lemon syrup and stir gently. Add more sparkling water to taste if needed. Pour the mixture into the glasses and serve immediately.